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AbstractTitanium alloy can be found in numerous applications, such as chemical, aerospace, and energy industries, among other sectors, due to its excellent performance. Nevertheless, the possible uses of a variety of titanium-based alloys have been greatly restricted by their low hardness and inadequate resistance to wear. Therefore, in this research work, WC–Cu composite electrode assisted electrical discharge coating (EDC) is used for improving microhardness (MH) and surface integrity of Ti–6Al–4V alloy. By utilizing powder composite electrode, the conductivity of the electrode can be increased, which provides controlled electric spark, resulting in uniform deposition. In order to increase the rate of deposition, the terminal of the EDM has been changed as WC–Cu composite electrode as anode and workpiece as cathode. Response surface methodology is used for studying the variables including compacting pressure (MPa), discharge current (I), pulse on time (Ton). In addition, microstructure, elemental analysis and coating interface of deposited Ti–6Al–4V alloy are investigated through scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The surface roughness of 8.86 µm was achieved at 400 MPa, 6 A, and 40 µs. The maximum MH of 988 HV was obtained at 400 MPa, 10 A, and 80 µs. The MH of the deposited layer is around 2–3 times harder than base material. Moreover, a greater adhesion strength coated layer was ∼118 N, which permits the alloy to have improved wear resistance. It was concluded that using a high-pressure electrode with lower settings resulted in an improved surface finish, while higher settings led to increased MH. [ABSTRACT FROM AUTHOR]

This work is devoted to studying the features of the generation of metal nanoparticles (NPs) by underwater discharges and their use in the technology of growing grain crops. The purpose of the study is to use the latest nano-containing preparations based on NPs of biofunctional metals, which will allow the introduction of modern technologies and technological processes for environmentally friendly crop production while simultaneously increasing the quality indicators of the final wheat harvest. To obtain NPs, metals of the biogenic group were chosen, the content of which in known agrochemical preparations is at least 0.01%. Metal NPs were obtained in discharge chambers filled with deionized water. As a result of underwater electric spark discharges, metal colloids were obtained as a preparative form of nanomaterials for further use and processing of wheat crops. To carry out the certification of NPs by the methods of electron microscopy (SEM and TEM) and X-ray structural analysis, the metal phase of the colloidal solutions was separated from the dispersion medium by drying. We determined the composition, structure, and average size of the target NPs. A complex preparation was studied, the composition of which included metal NPs, in particular Fe − 1800 ppm; Cu − 400 ppm; Zn − 1000 ppm; Mn − 800 ppm. Testing of the drug was carried out in field conditions during the cultivation of winter wheat at various stages of organogenesis. The application rate of the drug was 1–1.5 L/ha, accordingly, 1.0–1.5 L of the drug was diluted in 250 L of water. Foliar treatment of wheat plants was carried out. The analysis of grain quality indicators showed a 30% increase in the total protein content and a more than two-fold increase in gluten, which indicates the extraordinary prospects of using the obtained preparations. [ABSTRACT FROM AUTHOR]

This study utilized experimental methods involving high-speed cameras to observe the interaction between cavitation bubbles, generated by a low-voltage electric spark device, and particles near a rigid wall. The dynamic characteristics of the particles were analyzed under varying conditions, including different cavitation bubble sizes, particle sizes, and distances between the cavitation bubble and the wall. Two characteristic parameters were introduced: χ for the particle and cavitation bubble sizes, and λ for the cavitation bubble wall distance. Qualitative distinctions were made among types of particle–bubble interactions, and force analysis was conducted under conditions where χ exceeded the threshold χt. The findings reveal that when χ < χt, particle motion is primarily influenced by the jet effects produced by the cavitation bubble. Conversely, when χ > χt, particle motion is dominated by the radiation forces exerted by the cavitation bubble. Under jet-dominated conditions, particle trajectories were observed to be erratic and unpredictable. For cases where λ < 0, the high-speed jet directly impacts the particle. Conversely, for λ > 0, the jet's velocity decays rapidly upon reaching the particle. In scenarios dominated by radiation forces, the cavitation bubble drew particles away from the wall, followed by their free fall back toward it. The influence of gravity, buoyancy, bubble radiation force, fluid resistance, and virtual mass force on particles was studied when radiation forces prevailed. The acceleration formula for particles was derived through the application of the bubble dynamics equation and was refined based on experimental observations. [ABSTRACT FROM AUTHOR]

With the rapid development and application of hydrogen in the chemical and energy industry, the safety of hydrogen industrial facilities has been widely concerned. In this study, the safety of hydrogen accidently released from a high-pressure tube storage system (tube diameter:10 mm, storage tank volume:4 L) was explored experimentally. The combustion behavior of the transient hydrogen jet and explosion overpressure under self-ignition and electric spark induction were investigated. Besides, the explosion overpressure and jet flame evolution laws of the hydrogen cloud induced by the release of unsteady turbulent hydrogen jets into the open environment were analyzed. The results revealed that the peak value of hydrogen self-ignition explosion overpressure was higher than that of electric spark ignition overpressure. Compared with spark ignition, hydrogen self-ignition flame structures can be maintained for longer time. However, spark ignition at low release pressures was more likely to cause hydrogen ignition and explosion compared to self-ignition. Finally, the combustion behavior and potential hazards of the ignited free transient hydrogen jet under different ignition modes were analyzed. This study can provide a reference for the prevention and control of hydrogen explosion accidents in practice. • Hydrogen jet explosion can be induced by spark within 5D of the nozzle axis. • Comparing with spark ignition, self-ignition explosion had higher overpressure peak. • Self-ignition process was stable, but spark ignition was sensitive to the spark position. [ABSTRACT FROM AUTHOR]

Ways to increase the efficiency of the electric spark method of wastewater purification from heavy metal ions by increasing the stability of discharges and reducing energy losses are shown. General regularities of changes in the electrical characteristics of a multi-spark underwater discharge distributed in a layer of a mixture of iron and aluminum granules from the parameters of the discharge circuit have been revealed. The dependencies of the power amplitudes of electric spark discharges in a layer of metal granules on time under conditions of different combinations of inductance and capacitance of the discharge circuit are formalized, the regularities of energy input into working reactors to regulate the conditions and efficiency of purification are considered. [ABSTRACT FROM AUTHOR]

In the electric discharge machining process, the material is separated from the surface of the work piece by an electric spark, and in the presence of the dielectric material and tool electrode, changes are made on the surface of the work piece. In this project, we investigated the effect of dielectric material and brass tool electrode diffusion on the surface of carbon steel workpiece by means of quantmetric analysis, X-ray diffraction and electrochemical impedance spectroscopy. The effect of the parameters such as electric current intensity (I), pulse on time (ton), pulse off time (toff) and machining time (τ) on the composition of work peace, microstructure and electrochemical corrosion of machined work peace, were investigated. The results of quantmetric analysis showed that with the increase of machining parameters, the amount of diffused copper (from brass tool electrode) and carbon (from pyrolysis of flashing dielectric material) on the surface of machined carbon steel was increased. X-ray diffraction results confirmed that the formation of different phases such as Fe1.92C0.08, Cu4, Cu2 and Fe2 on the surface of workpiece, which was accordance with the quantmetric results. Electrochemical studies showed that during the EDM process, the electrochemical corrosion resistance was increased. [ABSTRACT FROM AUTHOR]

Electric Vehicles (EVs) are powered by a battery mounted in the vehicle, which powers the motor and drives the wheels. Most commercial EVs can be charged by plugging them into a charging station. Such conductive recharging has various drawbacks, including physical plugging of the cable, safety concerns, and charging time. Manually charging EVs might be dangerous due to the chance of an electric spark or disaster. Advances in Wireless Power Transfer (WPT) demonstrate the capacity to transfer significant amounts of electricity over short and medium-range distances. The ultimate purpose of this paper is to improve the efficacy of electric car wireless charging systems. Here, a hybrid optimization-based Artificial Neural Network (ANN) model is applied to improve the efficacy of the WPT model in EVs. To optimize the weights of the ANN classifier, a hybrid approach termed as Grasshopper-Assisted Elephant Herd Optimization (GA-EHO) method is proposed. The GA-EHO is derived through the hybridization of Elephant Herd Optimization (EHO) Algorithm and the Grasshopper Optimization Algorithm (GOA) techniques. Finally, the experimental study reveals that at 70% learning rate, the proposed ANN system achieves a minimal MSE value of 0.0528, which is lower than other current classifiers, such as SVM, LSTM, and CNN. [ABSTRACT FROM AUTHOR]

Goal. Calculation and experimental determination of middle speed vL of advancement of plasma leader channel of a pulse spark discharge in the long air interval of the double-electrode discharge system (DEDS) «tip-plane». Methodology. Bases of the theoretical electrical engineering and electrophysics, electrophysics bases of technique of ultra- and high-voltage and high pulse currents, bases of high-voltage pulse technique and measuring technique. Results. The close calculation and experimental method of determination of middle speed vL of advancement of plasma leader channel of an electric pulse spark discharge is offered in the long air interval of DEDS «tip-plane». This method is based on the offered calculation empiric formula for finding of the indicated speed vL and results of decoding of oscillograms of process of cut of in-use standard interconnect аperiodic pulse of over- and high-voltage of temporal shape of Tm/Тd≈200 μs/1990 μs of positive polarity at an electric hasp in indicated DEDS of long air intervals with their minimum length of lmin, numeral making 1,5 m (first case) and 3 m (second case). It is shown that middle speed vL of advancement in atmospheric air of front of plasma channel of positive leader of an electric pulse spark discharge in probed DEDS «tip-plane» for two considered applied cases at lmin=1,5 m of lmin=3 m numeral makes approximately vL≈(1±0,03)ꞏ105 m/s. The found numeral value of this speed vL well coincides with the known experimental information for speed of advancement of vL≈105 m/s in atmospheric air of plasma channel of negative leader for a long storm spark discharge in DEDS «charged cloud-earth». It is set that for the standard interconnect аperiodic pulse of high- and ultra-voltage of temporal shape of Tm/Тd≈200 μs/1990 μs of positive polarity middle value of aggressive strength Ed of high pulse electric field in the air interval of probed DEDS «tip-plane» numeral makes minimum length of lmin=1,5 m near Ed1≈360,8 kV/m, and for his minimum length of lmin=3 m of − Ed2≈313,4 kV/m. Originality. The comfortable is developed in the use and reliable in practical realization technicians-and-engineers calculation and experimental method of research in the conditions of high-voltage electrophysics laboratory of difficult electro-discharge processes of development of leader hasp of long air intervals and determination of minimum electric durability of air insulation of electrical power engineering and electrophysics equipment on working voltage of classes of 330-1150 kV. Practical value. Application in area of industrial electrical power engineering and high-voltage pulse technique of the got numeral electrophysics results and offered calculation and experimental method of determination of middle speed vL of advancement in atmospheric air of plasma channel of leader of a long spark discharge will allow, from one side, to deepen our scientific knowledges about a long electric pulse spark discharge in an air dielectric, and, from other side, to develop high-voltage electrical power engineering and electrophysics devices with enhanceable reliability of their work both in normal operation and malfunctions. References 20, figures 5. [ABSTRACT FROM AUTHOR]

The Gas Additive Powder Mix near Dry Electric Discharge Machining (GAPMND-EDM) serves a manufacturing purpose, specifically for cutting hard materials. This involves the removal of material from a workpiece via fusion, ablation, and evaporation caused by the heat energy generated through electric sparks during energy supply. The process offers several advantages in terms of performance and characteristics. This research project aims to optimize key process parameters, including material removal rate, surface roughness, residual stresses, and microhardness. The study employs a methodology that combines the standard deviation-based objective weighting method with GRA (Gray Relational Analysis) optimization to enhance the hybrid GAPMND-EDM process when applied to EN-31 material. Experimental runs were conducted to evaluate the impact of various input factors, such as pulse-on time, discharge current, dielectric fluid pressure, and metallic powder concentration. The taguchi-based GRA method was utilized for this purpose, and the experimental design followed an L-27 orthogonal array with the assistance of Minitab-19 software. A total of 27 experiments were performed, encompassing diverse combinations of process parameters. Subsequently, an ANOVA (Analysis of Variance) was executed to analyze the influence of pulse-on time, discharge current, dielectric fluid pressure, and metallic powder concentration on Material Removal Rate (MRR), Surface Roughness (SR), Residual Stress (RS), and Microhardness (MH). The result shows the optimal combination of parameters, denoted as A2B2C2D1, was identified as the preferred configuration. [ABSTRACT FROM AUTHOR]

Goal. Development of the generalized physical principle of development of plasma channel of a high-voltage electrical pulse spark discharge in the homogeneous dielectric of the different aggregate state. Methodology. Basis of physical optics, theoretical electrical engineering, electrophysics bases of technique of high-voltage and large pulse currents, bases of high-voltage pulse technique and measuring technique. Results. Development of physical principle of development of plasma channel of an electric pulse spark discharge is executed in a homogeneous gas dielectric on the applied example of the use in calculations and experiments of the double-electrode discharge system (DEDS) with a long air interval, testing action of standard interconnect аperiodic pulse of highvoltage of temporal shape of Tm/Тd≈200 μs/1990 μs of positive polarity. The generalized formula is got for the calculation of total length of lc of the real way of development of an pulse spark discharge in an air dielectric, which allowed to formulate the offered physical principle in the following kind: «The plasma channel of an pulse spark discharge in a gas dielectric spreads from one of its points to other after a way length of lc, providing the least falling on it of electric voltage of Uc». It is shown that this principle in the first approaching can be applied and to the homogeneous liquid and hard dielectrics. Comparison of the developed physical principle of distribution of plasma channel of an electrical spark discharge is executed in a dielectrical environment with fundamental Fermat physical principle (a law) for distribution of light in an optically transparent environment, which specifies on mathematical likeness and closeness on destiny of these physical principles. Calculation estimations of falling of electric voltage of Uc on total length of lc of the real zigzag way of development in the air dielectric of DEDS a «edge-plane» with the least length of its discharge interval of lmin=1,5 m is presented, that a value Uc does not exceed 9 % from the experimental level of aggressive voltage of Umd≈611,6 кV in this DEDS for the аperiodic pulse of voltage of Tm/Тd≈200 μs/1990 μs. It is set that the estimated time of td advancement of leader channel of electric pulse discharge in air DEDS (lmin=1,5 m) on its real way total length of lc≈1,53 m makes td≈15,3 μs, and experimental duration of cut of Tdc of the indicated аperiodic impulse of voltage utilized in experiments, characterizing time of short circuit by the plasma channel of discharge of air interval in DEDS, appears equal Тdc≈td≈17 μs. Originality. The generalized physical principle of development of plasma channel of a high-voltage electrical pulse spark discharge is first developed in the homogeneous dielectric of the different aggregate state. Practical value. Application in electrical engineering practice and high-voltage pulse technique of the offered principle of distribution in the dielectrics of plasma channel of an pulse spark discharge will allow to develop both new and to perfect the existent methods of computer design of electro-discharge processes in the gas, liquid and hard insulation of different high-voltage electrical power engineering and electrophysics devices, directed on the increase of reliability of their operation. References 25, figures 5. [ABSTRACT FROM AUTHOR]

The present study focuses on the examination of the combustion behavior of Iraqi LPG-air mixtures, flame propagation, and the tulip flame phenomenon in tubes. A new experimental facility was designed and constructed, featuring a complete setup comprising a combustion chamber unit, ignition unit, fuel injection and control unit, mixture preparation unit, and flame imaging unit. The combustion process was initiated through ignition by an electric spark, and both experimental measurements and numerical simulations were conducted using various turbulence models, including the realizable k-e model, the k-e model, and the Launder Sharma k-e model. The study aimed to compare and validate the numerical results with empirical observations, specifically focusing on flame propagation velocity, peak pressures, and tulip flame formation. The investigation revealed that the k-e model exhibited the closest agreement with experimental findings, accurately capturing flame propagation dynamics and tulip flame formation. However, discrepancies were noted in the numerical simulations, attributed to the absence of a wrinkling factor in the laminar combustion model, leading to smoother flame boundaries compared to experimental flames. The research highlighted the influence of turbulence on flame propagation beyond the tulip flame zone, necessitating further inquiries and model refinements to improve predictive capabilities. The findings affirm the appropriateness of the k-e model in simulating the combustion process and provide valuable information for optimizing combustion efficiency andmitigating pollutant emissions. Future investigations will be essential to enhance turbulence models and advance the understanding of flame dynamics in confined environments. The comprehensive analysis of flame behavior presented in this study contributes to the advancement of combustion science and engineering, offering potential applications in various industrial and environmental settings. [ABSTRACT FROM AUTHOR]

Miller and Urey applied electric sparks to a reducive mixture of CH4, NH3, and water to obtain a complex organic mixture including biomolecules. In this study, we examined the impact of temperature, initial pressure, ammonia concentration, and the spark generator on the chemical profile of a Miller–Urey-type prebiotic broth. We analyzed the broth composition using Gas Chromatography combined with Mass Spectroscopy (GC/MS). The results point towards strong compositional changes with the nature of the spark. Ammonia exhibited catalytic properties even with non-nitrogen-containing compounds. A more elevated temperature led to a higher variety of substances. We conclude that to reproduce such a broth as well as possible, all the studied parameters need to be tightly controlled, the most difficult and important being spark generation. [ABSTRACT FROM AUTHOR]

Understanding how dust can ignite and explode in an industrial contest is an important and complex task, and much of the work around this is mainly performed via experimental measurements, in accordance to specific standards. However, those same properties are straightforwardly closely related to the nature of the experimental tests. Among these, the Minimum Ignition Energy (MIE) of a dust cloud, that is usually measured in a MIKE 3 apparatus, can be affected by several factors, as: delay time of the electric spark with respect to the dust-air dispersion formation inside the apparatus, dust concentration, humidity content, dust granulometry, etc. The delay time is one of the worst parameters to adjust, because the fluid-dynamics of the dust-air mixture inside the tube is not easily predictable. Within this work, a study on the characteristic times of all the relevant phenomena occurring within a MIKE 3 apparatus was done by means of slow-motion videos of the tests. Particularly, three different characteristic times were compared referring to a given sample of niacin dust: dust lifting and settling times, effective spark delay time (that is, the time at which the spark is visible) and combustion time (that is, the time at which the flame is visible). According to the results, the effective delay time is almost always quite different with respect to the theoretical one, influencing the effective concentration of dust between the electrodes and, finally, the possibility to have a flame ignition or not within the apparatus. This means that the value of the MIE parameter can be profoundly influenced by the effective delay. [ABSTRACT FROM AUTHOR]

Spectral characteristics of ultrahigh-frequency radiation generated by a pulsed electric spark in a millimeter air gap are studied, together with its temporal correlation with the behavior of the discharge current and voltage in a nanosecond time scale. Systematic features of the UHF emission and general picture of possible phenomena in the spark gap are discussed. [ABSTRACT FROM AUTHOR]

The explosion process of the flake aluminum powder–air two-phase flow is experimentally studied in a large-scale long straight horizontal tube with a length of 32.4 m and an inner diameter of 0.199 m. The deflagration-to-detonation transition (DDT) of the aluminum powder–air mixture is analyzed after being ignited by a 40-J electric spark, and the DDT of the mixture at different mass concentrations is compared. The results show that self-sustained detonation can be achieved in the range of 286–532 g/m3 of the flake aluminum powder concentration, and the DDT process of the aluminum powder–air mixture at the concentration of aluminum particles 409 g/m3 (optimal concentration) is analyzed in detail. The detonation velocity and detonation pressure at the optimal concentration are 1690 m/s and 58 bar, respectively. During the self-sustained detonation stage, the detonation overpressure of the multiphase fuel–air mixture exhibits a typical constant oscillation characteristic, while the detonation velocity remains stable. In addition, a double-headed mode helical detonation phenomenon is observed in the detonation wave front of the aluminum powder–air mixture. The structure of the detonation wave, the flow field parameters, and the interaction between the shock wave and the three-wave point trajectory are analyzed. The detonation cell size at the optimal concentration is approximately 486 mm. [ABSTRACT FROM AUTHOR]

A schematic diagram of position-sensitive luminescent spark sensors with a spectral radiation converter is considered. By using the sensor, it is possible to detect an electric spark by one or two spatial coordinates depending on the location of the ends of optical fibers. Numerical simulation and optimization of optical systems of position-sensitive luminescent spark sensors has been carried out. The efficiency and resolution of the optical system have been calculated. [ABSTRACT FROM AUTHOR]

Today, there is a sharp struggle for demanded and competitive products all over the world. The existing traditional production technologies have exhausted their possibilities. New technologies should be based on high energy technologies. One of such technologies is plasma technologies. Among the plasma technologies for hardening metal surfaces, the most suitable is the hardening technology using electric spark discharges. However, these technologies do not currently have process optimization. This article proposes one of the options for solving this problem by simulating the process of electrospark alloying of elements of refractory materials into the surface layer of samples of real parts of machines and mechanisms, which are models of these parts. [ABSTRACT FROM AUTHOR]

In this work, a number of significant factors are highlighted that affect the optical emission spectrochemical tests with spark or electric arc excitation on stainless steels with multiple synergistic purposes such as: acquiring new knowledge, increasing the amount of information obtained about the material, increasing the efficiency and quality of the tests, the characterization of special purpose alloys and the assessment of their compliance with the specified requirements. In this direction, it requires both knowledge of testing methods (theoretical basis, test method, procedure related to the method, quality assurance testing) and the characteristics of the investigated materials. These aspects are necessary for the analysis of the test system and the most correct preliminary interpretation of the experimental results. [ABSTRACT FROM AUTHOR]

This paper presents data on investigation of the pseudospark switch whose trigger unit uses a low-current auxiliary glow discharge with hollow cathode and hollow anode. The electrode system of this unit communicates with the main high-voltage gap of the switch due to the aperture in the flat part of one of the trigger electrodes. It is shown that when the electrode with the aperture plays of role of the hollow cathode of the auxiliary discharge, a low parasitic current through the aperture is provided by the ion flow. This ion current does not practically influence on the static breakdown voltage of the main gap. Applying the trigger pulse between the trigger electrodes leads to the pulsed trigger discharge with an enhanced current. At a negative polarity of the trigger pulse, the cavity with aperture turns out into the hollow anode so that the current is able to be intercepted through the aperture to the grounded cavity of the main gap. The plasma is generated in the cavity and the switch is triggered. With the proper selection of the geometry of the trigger electrodes, the delay time to trigger at a level of several tens of nanoseconds is achievable. [ABSTRACT FROM AUTHOR]

Electrical discharge in liquids is a research field that has great potential in environmental and technological applications. Depending on the experimental conditions (liquid nature, interelectrodes distance, applied voltage, pulse width, etc.), various discharge modes can be obtained. The involved physical processes have relatively fast spatiotemporal dynamics and, therefore, are not well understood. In this study, we report the electrical characterization, coupled with time-resolved light detection (using a photomultiplier, PM, tube), of positive and negative pulsed nanosecond spark discharges in de-ionized water using copper electrodes (distanced by ∼50 μm) in a pin-to-plate configuration. A detailed analysis of the current–voltage waveforms during the pre-breakdown and the breakdown phases is shown, and we found that the pre-breakdown phase depends on the high voltage magnitude only for positive polarity. On the other hand, the PM signals showed dependence on the voltage magnitude and on the pulse width, and various emission phases are observed. These phases can be related to the discharge power and/or to the discharge current. Filtered PM signals at various wavelengths are also acquired, and their temporal dynamics are discussed regarding the discharge conditions. [ABSTRACT FROM AUTHOR]

The electric-spark initiation of thermite mixtures based on nanosized powders of aluminum and copper oxide has been studied. Data on the effect of the electric spark discharge energy on the ignition delay were obtained. During the initiation of long cylindrical samples of mixtures with a low-current spark, two types of unsteady combustion were observed. The first type is characterized by the exponential establishment of constant burning rate. The second type is characterized by regions with incomplete reaction in the main propagation direction. To obtain steady combustion of a thermite mixture with a minimum ignition delay time, it is necessary to use a discharge energy of more than 5 mJ per 1 mm2 of the mixture surface. [ABSTRACT FROM AUTHOR]

The nitration of phenol with plasma-activated water (PAW) generated by pulsed radiation of an electric spark discharge has been studied. Long-lived nitrogen-containing active species that accumulate in water during treatment are nitrous acid and the ...ONOOH/ONOO− complex, which decomposes into peroxynitrite and peroxynitrous acid. Their concentration in PAW after 10 min of treatment was ~10−3 mol/L. When PAW is mixed with phenol in a 1 : 1 ratio, the identified reaction product is 4-nitrophenol. The yield of nitration through PAW is equal to the nitration yield by the direct action of hot plasma radiation on a phenol solution. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Mine Automation is the property of Industry & Mine Automation Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Impulsive underwater discharges have been investigated for many decades, yet the complex pre-breakdown processes that underpin their development are not fully understood. Higher pre-breakdown energy losses may lead to significant reduction in the magnitude and intensity of the pressure waves generated by expanding post-breakdown plasma channels. Thus, it is important to characterize these losses for different discharge types and to identify approaches to their reduction. The present paper analyses thermal pre-breakdown processes in the case of free path and wire-guided discharges in water: fast joule heating of a small volume of water at the high-voltage electrode and joule heating and the melting of the wire, respectively. The energy required for joule heating of the water and metallic wire have been obtained from thermal models, analysed and compared with the experimental pre-breakdown energy losses. Pressure impulses generated by free path and by wire-guided underwater discharges have also been investigated. It was shown that wire-guided discharges support the formation of longer plasma channels better than free path underwater discharges for the same energy available per discharge. This results in stronger pressure impulses developed by underwater wire-guided discharges. It has been shown that the pressure magnitude in the case of both discharge types is inversely proportional to the observation distance which is a characteristic of a spherical acoustic wave. [ABSTRACT FROM AUTHOR]

Spark plasma sintering (SPS) is a new sintering method having shorter sintering time and higher densification speed than the traditional sintering methods. In this paper, the Si3N4/TiC ceramic tool material is sintered by SPS. The microstructure and mechanical properties of the material under different sintering parameters are compared. The sintering process of the material is then analyzed, and the best sintering parameters are obtained. Heat the material to 1600°C and keep the temperature for 15 min, then continue to heat to 1700°C and keep the temperature for 10 min, Si3N4/TiC ceramic tool material has high mechanical properties, its bending strength, fracture toughness, and Vickers hardness are 959 MPa, 8.61 MPa·m1/2, and 15.21 GPa, respectively. The scanning electron microscope (SEM) analysis shows that under this condition, the sintering additives and Si3N4/TiC material form the liquid phase, which makes the Si3N4 particles rearrange, dissolve, precipitate, and transform into rod shape β‐Si3N4. In addition, under the action of pulse current and external pressure, electric sparks are generated between TiC particles, which allows the material transfer and particle refinement. Therefore, the β‐Si3N4 has uniform grain size, and it is vertically and horizontally arranged in the structure, which makes the material have excellent mechanical properties. [ABSTRACT FROM AUTHOR]

This work is devoted to the plasma diagnostics of an underwater electric spark discharge, specially developed for the synthesis of metal nanoparticles by electro erosion of metal granules immersed into water. To improve the process of metal nanoparticle generation, the main plasma parameters for different modes of discharges between molybdenum and, separately, iron granules were investigated. The optical emission spectroscopy as a non-perturbing method was used. Namely, the Boltzmann plots on the basis of metal atomic lines' (in particular Fe I and Mo I) intensities are used to determine the electron temperatures in plasma. Profile of Hα spectral line, exposed to the Stark mechanism of spectral lines' broadening, is used to determine the electron density in such plasma. The black-body radiation is found in the spectrum of the discharge between molybdenum granules. It was found that the background emission in the spectral regions with densely spaced spectral lines can be caused by the overlapping of spectral lines' contours for the underwater discharge between metal granules. [ABSTRACT FROM AUTHOR]

Copyright of Machine Tool & Hydraulics is the property of Guangzhou Mechanical Engineering Research Institute (GMERI) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Underground utility tunnels (UUTs) are convenient for the integrated management of various infrastructure facilities. They ensure effective control of underground facilities and reduce occupied space. However, aging UUTs require effective management and preventive measures for fire safety. The fundamental problems in operating UUTs are the frequent occurrence of mold, corrosion, and damage caused to finishing materials owing to inadequate waterproofing, dehumidification, and ventilation facilities, which result in corrosion-related electrical leakage in wiring and cables. To prevent this, an abnormal sound detection technology is developed in this study based on acoustic sensing. An acoustic sensor is used to detect electric sparks in the moldy environments of UUTs using a system to collect and analyze the sound generated in the UUTs. We targeted the sound that had the highest impact on detecting electric sparks and performed U-Net-based noise reduction and two-dimensional convolutional neural network-based abnormal sound detection. A mock experiment was conducted to verify the performance of the proposed model. The results indicated that local and spatial features could capture the internal characteristics of both abnormal and normal sounds. The superior performance of the proposed model verified that the local and spatial features of electric sparks are crucial for detecting abnormal sounds. [ABSTRACT FROM AUTHOR]

The moment of resistance to cutting during milling of pine and oak along and across the fibers, depending on the dry or wet state, with a disc-shaped milling cutter made of 9KhS steel with an electric-spark coating applied to the teeth, was investigated. The influence of electric spark coatings of different structural and phase composition, obtained by electrodes made of T15К6 hard alloy and the Fe–Mn–C–B and Fe–Cr–C–B powder wires on the force indices of the milling process of wooden materials was analyzed. [ABSTRACT FROM AUTHOR]

In this paper, a radio frequency identification (RFID) tag is designed and fabricated based on highly electrical and thermal conductive graphene films. The tag operates in the ultrahigh-frequency (UHF) band, which is suitable for high-power microwave environments of at least 800 W. We designed the protection structure to avoid charge accumulation at the antenna's critical positions. In the initial state, the read range of the anti-high-power microwave graphene film tag (AMGFT) is 10.43 m at 915 MHz. During the microwave heating experiment, the aluminum tag causes a visible electric spark phenomenon, which ablates the aluminum tag and its attachment, resulting in tag failure and serious safety issues. In contrast, the AMGFT is intact, with its entire read range curve growing and returning to its initial position as its temperature steadily decreases back to room temperature. In addition, the proposed dual-frequency tag further confirms the anti-high-power microwave performance of graphene film tags and provides a multi-scenario interactive application. [ABSTRACT FROM AUTHOR]

Flammable gas leaked from pipelines is easy to cause explosion accident. The consequences of accident are amplified in strongly constrained environments near the pipelines. In this paper, a gas leakage and explosion accident in Beijing is analyzed using field investigation and relevant experimental analysis techniques, and the complete investigation process of accident cause based on physical evidence is displayed. Some theoretical analysis models are introduced to explore the causes of this type of accident from a system perspective. The laws of explosion damage of building structures in strongly constrained environments are also summarized. The results indicate that the gas leaked from the end of the hose was excited by an electric spark in the electrical box causing this explosion and a gas explosion with a TNT equivalent of 2.73–4.28 kg is sufficient to damage a large number of walls of civilian buildings. The pressure difference between the two sides of structures and the duration are decisive factors in the degree of damage. Cause analysis shows that human error needs to be avoided through education and supervision. The study can provide theoretical references for the investigation of explosion accidents, as well as improvement of energy management system. [ABSTRACT FROM AUTHOR]

An analytic methodology is presented to reconstruct the pressure waveform of flowfields with circular symmetry from the phase shift detected with Focused Laser Differential Interferometry (FLDI). A weak blast wave generated by an electric spark in ambient air is investigated with the proposed approach. Values of separation distance between the differentiating foci of the FLDI Δx of 76, 120, 175, and 252 μm are employed to probe the flowfield at locations between 3 and 50 mm from the spark source. In a subset of these distances, reference measurements of peak pressure obtained with a surface pressure sensor indicate good agreement with the reconstructed data when small separation distances are used. Further analysis of FLDI reconstructed data is conducted using theoretical correlations for N-waves in terms of the distribution of pressure peak amplitude and compression phase as the wave front propagates. Agreement with theory is verified for all differentiation separation distances except the largest, for which peak pressure comparison shows a 10% loss of measured vs predicted value. A computational FLDI is employed to scrutinize the simplifying hypotheses supporting the waveform reconstruction approach. The direct comparison between experimental and computational FLDI output reveals additional discrepancies for intermediate Δx values but very good agreement for the smallest Δx. The proposed methodology is thus verified to be reasonable, upon appropriate minimization of the FLDI differentiation distance. A parametric analysis using computational FLDI indicates the adequate value of FLDI Δx to be 20% or less of the flowfield characteristic length in terms of density gradient. [ABSTRACT FROM AUTHOR]

In this paper, the effects of pulse voltage rise time on the nanosecond pulsed breakdown of the nitrogen spark switch at atmospheric pressure are analyzed. Based on the assumption of initial electrons generation due to the field emission, the simulations are performed using a three-dimensional particle-in-cell, Monte Carlo-collision model for the pulse voltage with a rise time of 40, 60, and 100 ns, respectively. The breakdown experiments of the nitrogen spark switch are carried out for three different rise times. The results obtained are as follows. First, the nanosecond pulsed breakdown of the switch includes the formation and fast propagation of the streamer, which depend on the multiplication of the electron avalanche, and the intense ionization due to photoelectrons and energetic electrons, respectively. Second, with the rise time of pulse voltage increasing, the generation of runaway electrons becomes more difficult and the streamer branches, which are mainly caused by photoionization and captured energetic electrons, become more obvious. Finally, the breakdown time delay of the switch becomes shorter and the breakdown voltage becomes higher at the same pressure for the decreasing rise time of pulse voltage, which is consistent with the measurement results. [ABSTRACT FROM AUTHOR]

The article considers the efficiency of applying electric spark coatings with the aim of studying the effective influence on the tribological properties of eutectic alloys. Friction and wear tests of electrospark coatings made of the developed eutectic alloy on a steel substrate were performed. In order to compare the effectiveness of the influence on the tribotechnical properties of eutectic alloys, both the coatings in the initial state and the coatings annealed under two different modes were tested. Based on the results of the study of the chemical composition of the films formed in the process of friction, regularities were established by qualitative assessment. The dependences of tribotechnical properties for the initial and heat-treated coatings were determined. These studies indicate the feasibility of using electrospark coatings for different friction conditions. [ABSTRACT FROM AUTHOR]

Combustible gas explosions are typically triggered at high temperatures by the generation of electric sparks on starting, stopping, or short circuiting of electrical equipment. Flameproof enclosures are widely installed in the petrochemical industry as safety equipment for eliminating ignition sources. Such enclosures are designed with a double-cavity structure, and a hole plate is used to connect the two cavities. However, pressure piling occurs in such double-cavity-connected structures, resulting in flameproof enclosures requiring to bear higher pressure than designed, which is a safety hazard. However, few studies have focused on the effect of the diaphragm orifice diameter of flameproof enclosures. Because the explosion of combustible gas in a flameproof enclosure is a complex process, numerical simulation was performed to study the process. Fluent was used for numerically simulating the ethylene/air premixed gas explosion characteristics of double-cavity-connected structure flameproof enclosures. The effects of an orifice hole diameter from 10 mm to 45 mm on flameproof characteristics, including the maximum explosion pressure, maximum explosion pressure rise rate, and maximum explosion index, were examined. The results are critical for the effective design of a double-cavity flameproof shell and provide theoretical support for fire suppression in a flameproof enclosure. [ABSTRACT FROM AUTHOR]

The Ti-based metal matrix composite samples are novel, fabricated by using high voltage electric discharge and spark plasma sintering processes. They have potential usage in the aviation industry. A research that allowed measuring an electrical conductivity of Ti-based composites was performed. A collinear four-point probe method was chosen for measurement of electrical conductivity. Needlelike probes were used to contact the tested sample. Other aspects of the measurement setup are discussed and selected according to relevant literature. A simulation was performed using COMSOL software to validate the measurement method. Furthermore, a simulation performed for contact force of the probes was performed. A 3D model of the measurement tool was created and designed. The measurement setup was tested and validated by using a copper sample. electrical resistance of Ti-based composite samples was measured, and electrical conductivity was calculated. Furthermore, samples were measured at different temperatures and resistivity dependence to temperature was presented. Experimental results are compared to similar research results. [ABSTRACT FROM AUTHOR]

Silicon nano- and microparticles obtained using electric-spark dispersion of silicon electrodes and granules in 40 wt% solution of methyl alcohol in water were investigated by ultrasoft X-ray emission spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, scanning and transmission electron microscopies. In addition, the SiLα spectra of obtained silicon particles were modeled by superimposing the spectra of pure silicon and silicon oxide taken in certain weight ratios. It was found that the surfaces of Si nano- and microparticles obtained in 40 wt% solution of methyl alcohol in water are covered with silicon oxide and chemisorbents, while the core consists of crystalline silicon with a cubic face-centered lattice. The silicon nano- and microparticles show potential as an anode material to replace commonly used graphite electrodes. The charge capacity of the electrode based on mixture of Si nano- and microparticles with graphite powder was about 1272 mAh/g after ten cycles. [ABSTRACT FROM AUTHOR]

In this paper we analyze the possibilities of using machine learning algorithms for analysis of optical spectra of electric discharge spark in atmosphere. Breakdown in air can be initiated by intense laser pulse, making plasma which has a significant electrical conductivity. The formed plasma can be further maintained by electric current obtained from capacitor discharge. In such a case the capacitor voltage can be much lower than the striking voltage (the voltage needed to initiate the electric breakdown in air). Present setup has timing precision and low jitter of fast laser and arbitrary high energies corresponding to capacitance and voltage to which the capacitor is charged. We have used a streak camera equipped with a spectrograph to analyze optical emission of plasma obtained in this way. Q-switched Nd:Yag laser was used to achieve the initial breakdown in air. Machine learning methods were used in order to classify optical spectra of plasmas with different electron temperatures obtained with different excitation energies. We have shown that, instead of using the usual way of identifying the spectral peaks and calculating their intensity ratio, it is possible to train the computer software to recognize the spectra corresponding to different electron temperatures. Principal component analysis was used to reduce the dimensionality of problem. We present possibilities of plasma electron temperature estimation based on several clustering algorithms. [ABSTRACT FROM AUTHOR]

Herein, the breakdown mechanism of alumina‐based ceramics (Al2O3–ZrO2) is studied. The specimens are characterized for their density, phase structure, micromorphology, breakdown process, and breakdown channel by micro computed tomography, high‐speed cameras, etc. The study reveals that the dielectric breakdown stability of the samples shows a decreasing trend and the dielectric loss shows an upward trend with the increase of ZrO2 content. The tetragonal phase zirconia is beneficial to enhance the dielectric breakdown strength of the sample, which is related to the martensitic transformation to prevent crack propagation. Before the ceramic breakdown, the insulating oil first breaks down, causing electric sparks. Once the ceramic breakdown occurs, the charges are rearranged, and a large amount of heat energy is generated instantly to melt the substance around the breakdown channel and erupt to the surface to form pits under the action of high internal stress. [ABSTRACT FROM AUTHOR]

Aluminum 6061-T6 alloy is widely used in several manufacturing sectors like automotive, aerospace and marine industries owing to their unique characteristics of high strength to weight ratio, low density and supreme electrical and thermal conductivity. Some of the properties of Al 6061-T6, such as poor surface and tribological behaviors, make them unable to be used in critical parts. In this work, surface modification was performed for Al 6061-T6 using WS2 solid lubrication through the electrical spark deposition technique. The deposition was conducted by altering three different parameters, that is, powder concentration (PC), spark-on time (ST) and gap voltage (GV), based on the Box–Behnken design of response surface methodology. Effects of these deposition parameters were investigated on various surface modification aspects, including deposition rate, surface roughness (SR), microhardness and layer thickness. Results exhibit that the WS2 deposited surface significantly improved the surface characteristics. Material deposition rate predominantly increased with an increase in PC. Surface microhardness is enhanced by 9–20 times that of the base material. The lowest SR was attained at an intermediate level of PC with a low level of ST and GV. A minimum layer thickness of 32.12 μ m at intermediate PC and high ST with low GV was achieved. The elemental and structural analyses confirmed that the formation of intermetallics, such as WO2, WO3, Al2O3 and Al4C3, was formed during electrical spark deposition. [ABSTRACT FROM AUTHOR]